We've build our own automated hosting infrastructure* a few years ago on top of libvirt. Using the libvirt API was a breeze and libvirt is rock solid since day one for us, I can only recommend this project.

* Shameless plug: https://github.com/OnitiFR/mulch

We're using libvirt-go binding (Daniel Berrangé and his team is doing a excellent job maintaining it!), and KVM/QEMU hypervisior. For a small team like us, it's incredibly valuable to have access to such powerful tools in a such easy way.